The growing sophistication of philosophical speculation together with the increasingly contentious claims of the thirteenth-century masters of Arts and Theology is reflected in the literary career of Robert Kilwardby. As a young Parisian Arts master, Kilwardby devoted much of his energy to explaining the works of Aristotle, recently introduced into the University’s curriculum. Although particularly interested in the logical treatises, Kilwardby most likely commented upon the so-called ‘Ethica vetus et nova’, which were part of the Arts curriculum in the first half of the thirteenth century. Kilwardby’s commentary, while quickly superseded by the more complicated questions on the entire Ethics, represents an extremely important transitional phase in the understanding of Aristotle’s moral philosophy. Kilwardby’s careful reading of Aristotle’s text allowed him to reject the usual religious interpretation of his contemporaries. His awareness of the limitations of moral science marks a decisive step away from the earlier reading of the Nicomachean Ethics (EN), which viewed Aristotle’s doctrine of the human good to be identical with the religious ideal of union with God. As a result, Kilwardby’s commentary on the EN demonstrated how Aristotle’s ethics could no longer be understood as a slight variant of Christian moral theology.